The present invention relates to a cable joint for connecting power cables. In a conventional cable joint for connecting power cables, each cable having a conductor successively surrounded by a first insulation layer, a semi-conductive layer, a metallic screen, and a second insulation layer, the cable joint including a junction body comprising connection means for connecting bared portions of the conductors together at the terminus of each cable and first insulation means for surrounding the connection means, the cable joint further including a metallic member forming a shield over the junction body, and second insulation means covering the metallic member as well as end portions of the second insulation layer of the power cables, the metallic member having at least two parts electrically separated by a shield break and each provided with a terminal electrically coupled to the metallic screen of a distinct one of the power cables.
In such a known cable joint, a pre-moulded junction body is surrounded by a metallic member that is a metallic tube narrowed and soldered on both ends of the joint to the metallic screens of the cables. The shield break is an interruption of this tube and comprises an insulating flange of about 300 mm in length located over the connection means. This insulating ring is bolted between the two parts of the metallic tube. The cover formed by the metallic member, with the insulating ring, is filled with glass pellets to improve heat conductivity. The terminals of the two parts of the metallic member are used for grounding connections and/or for cross-bonding the metallic screens. The reason for such connections is that, for instance, in case of three single-core power cables making up a three-phase cable installation, the currents that are induced in the metallic screens of the cables may become intolerably high. These induced currents may be eliminated by dividing the metallic screens into isolated sections that are cross-bonded. To this end, conductors interconnect the terminals of the metallic members of the different cables. The conductors are constituted by 2 single-core cables or by a coaxial cable of which at least one part runs on top of the metallic tube to access the terminal located at an end of the junction body. The connections, cables and the whole metallic member are covered by a polyester box completely filled with a polyurethane resin to provide mechanical protection and electrical insulation, this box constituting the second insulation means.
In this known type of cable joint, the amount of resin to be cost in the field between the metallic member and the second insulation means for insulating and protecting the metal cover and the conductor(s) running thereon is relatively important. The cable joint is thereby relatively expensive, its weight is high and it has a large external diameter.
Another type of known cable joint is for instance the "Cross-bonding joint 123 kV" type: MP1.123-31/32 of "CORTAILLOD COSSONAY CABLE". In this other known cable joint, a pre-insulated metallic tube is used for covering the whole junction body. At one end of the cable joint, the tube is soldered to the metallic screen of the cable, whilst at the other end of the cable joint, a relatively big epoxy insulator surrounds the other cable and is partially engaged into the metallic tube. This epoxy insulator has embedded two conductors electrically separated from each other and connected to terminals. One terminal is electrically connected to the metallic tube, whilst the other terminal is soldered to the metallic screen of the other cable. The embedded conductors extend out from the epoxy insulator, diametrically opposed, at the same end of the cable joint where grounding connection and/or cross-bonding is then possible. Because of the pre-insulated metallic tube, constituting the metallic member together with the second insulation means, no polyurethane resin is needed. However, the weight of the casing and the epoxy insulator is high. As a consequence, it is relatively difficult to handle the parts of this cable joint. Moreover, grounding connection and/or cross-bonding can not be done by means of a coaxial cable because the terminals, and thereby also the conductors, are diametrically separated in the epoxy insulator. This known cable joint is further relatively expensive because of the materials used therein.
It is further to be noted that in this known implementation, no filling material, such as glass pellets, is used between the metallic tube and the power cable. The thermal conductivity of the cover is thus bad because of the air gap created between the junction body and the metallic tube.